(1) Field of the Invention
The present invention relates to the general technical field of equipments used for flight guidance.
The invention concerns more particularly a method for presenting attitude and heading information of a vehicle and artificial spatial attitude and heading indicators or instruments of vehicle.
(2) Description of Related Art
The term “vehicle” encompasses any type of aircrafts or spacecrafts.
Different terms are used and for which the meaning is given by the definitions as follows:                2D: two dimensional,        3D: three dimensional,        AHRS: attitude and heading reference system,        CDI: Course Deviation Indicator        EFIS: electronic flight information system,        Heading: Direction with reference to the magnetic field of earth, or with reference to any other horizontal information.        IFR: Instrument Flight Rules,        ROC: rate of climb.        
The pilot of an aircraft needs in general many aircraft and environment data for taking the optimal decisions during his flight, especially in emergency situations. Among these data, there is for instance the aircraft attitude information such as pitch and roll information.
During the flight, the pilot should be aware of the instantaneous situation, such as e.g. altitude, airspeed and attitude under IFR conditions in order to determine the flight path and motion of the aircraft. The current state of the art equipments, however, cannot provide such instantaneous situation awareness. These known equipments, either providing inside-out or outside-in view, do not present the vehicle or aircraft's attitude in relation to the reference system, e.g. the orientation compared to the earth's surface.
It can occur that the pilot can see only the earth or only a blue sky in his primary flight display of the known equipments and that he cannot easily know in which direction he should steer to get a normal level of flight attitude.
By inside-out, one should understand that the aircraft symbol remains fixed while the background and horizon indicators move to indicate the aircraft attitude.
By outside-in, one should understand that the aircraft symbol moves in the same apparent direction as the aircraft is actually moving.
It is known to present horizontal information on a flat depiction in either inside-out or outside-in view. Both solutions lack a certain spatial orientation information as soon as the depiction limits are reached.
The depiction limits addressed with this invention are the fact that the projection of the 3D spatial situation on a flat area does reduce the information transmitted. The usual model to depict an attitude is to use a cylinder, sphere or similar which is divided into two equal parts. Both parts are painted in different colours, normally blue for the sky (upwards) and brown for the earth surface (downwards). When projecting this model onto the 2D screen area and taking into account that the object is not fully visible, but only a small viewport as selected by the designer of the artificial horizon, there are possible modes in which only one part of the model sphere is projected.
Those modes are lacking any information about the actual attitude or directions to correct the attitude. Means to overcome such situations have been developed in the past and lead to the introduction of flight director bars in the attitude indication.
A typical and known presentation of an artificial horizon will be for example an inside-out view projected onto a 2D (two dimensional) screen picture. The attitude indication provided by an inside-out view on a known artificial horizon has led to some abnormal situations and was so not considered as satisfactory.
Another kind of presentation currently used is an outside-in view, still projected on a 2D presentation.
The presentation of the 3D spatial orientation on a 2D projection lacks information as soon as the projection is full by either the sky or the earth. In such a case markings or other clues need to be added in order to provide the necessary orientation information for undertaking corrections. In high workload situations, such markings can easily be neglected by the crew as they might be occupied by other distraction coming from the aircraft or from the environment.
None of the above mentioned known indicators (inside-out or outside-in) are therefore satisfactory. Additional guidance information needs always to be introduced which is conclusive only after intensive training of the pilot.
An exemplary embodiment of a known attitude indicator is described in document U.S. Pat. No. 4,563,742, which discloses an attitude indicator combining the best features of both the inside-out and outside-in viewing modes. The aircraft symbol is positioned in accordance with the pitch of said aircraft and a horizon indicator is also positioned in accordance with the pitch of said aircraft. In this embodiment, there is a need of the two information elements, the pitch, which renders such a solution relatively complex. The drawback for this solution is the overlay of two moving elements, one representing the horizon, in order to provide the expected inside-out view and a movement of the aircraft pictorial, which will move in the opposite direction of the horizon. In addition, this principle is limited in feasibility to attitude situations which are not adverse, like e.g. nose fully up. Additionally the overlay of a moving object over the attitude presentation can result in misleading interpretation in case of high workload situations. The presented solution lacks also the immediate information about the corrective actions to be taken in adverse situations.
The document EP 0383083 A1 discloses an instrument with a fixed aircraft symbol and a reference system for flightpath control, in which information on the respective flight attitude is also integrated and thus flying manoeuvres can also be controlled at very high angles of attack.
Another exemplary embodiment of known attitude indicator is described in document U.S. Pat. No. 5,181,028, which discloses an attitude indicator with the use of shutter goggles and a fixed 3D aircraft presentation on a 3D display. The cost of such an instrument or indicator is therefore relatively high. This solution lacks simplicity as it requires several hardware items to work together. With malfunction of the goggles, which might not be feasible to be used during night flights, the crew is back to the classical presentation of attitude. Additionally the usage of goggles impairs problems and incompatibilities with other indicators in the cockpit, as it will filter wavelength or polarization, independently from the source of information, and has to be applied for usage with elements based on polarization, i.e. LCD displays.